The present invention relates to a technique of liquid crystal display(LCD) with a counter electrode and a pixel electrode capable of minimizing an area on which liquid crystal molecules do not operate, thus improving an aperture ratio and a transmittance of the LCD.
In general, an IPS-LCD (In-Plane Switching Liquid Crystal Display), improving a narrow viewing angle of a TN-LCD (Twisted Nematic Liquid Crystal Display) has a counter electrode disposed on a lower substrate on which a pixel electrode is arranged. That is, the electric field of the IPS-LCD is parallel to the upper and lower substrates while in the conventional TN-LCD, there is generated an electric field between the pixel electrode formed on the lower substrate and the counter electrode formed on the upper substrate, perpendicular to the upper and lower substrates.
With reference to FIG. 2, the IPS-LCD is described.
The LCD includes a gate bus line 1 made of opaque metal, for selecting a corresponding unit cell, a data bus line 3 made of opaque metal, a thin film transistor (TFT), a counter electrode 5 and a pixel electrode 6. Generally, the gate line 2, the data line 3, the TFT, the counter electrode 5 and the pixel electrode 6 are formed on a lower substrate 1. The data bus line 3 vertically intersects with the gate bus lines 2 in an uniform distance, thereby forming a space for a LCD unit cell. A channel layer 4 of the TFT is formed at the intersection of the gate bus line 2 and the data bus line 3. The data bus line 3 is overlapped with the channel layer 4 over the channel layer 4 and the gate bus line 2 is overlapped with the channel layer 4 under the channel layer 4. In the space for LCD unit cell, there are provided the counter electrode 5 and the pixel electrode 6. The counter electrode 5 has a wiring part 5a parallel disposed to the gate bus line 2 and at least one branch 5b extended from the wiring part 5a toward the gate bus line 2 with parallel to the data bus line 3. The number of branch 5b in the FIG. 1 is three and a distance between the branches is uniform. The wiring part 5a of the counter electrode 5 is connected to the wiring parts of left and right unit cells and all the counter electrodes receive same signal voltage. The pixel electrode 6 includes a first part 6a, overlapped with the channel layer 4 and serving a drain of the TFT, a second part 6b disposed between the branches 5b of the counter electrode 5 and parallel to the branch 5b and a third part 6c parallel to the gate bus line 2 for connecting the first part 6a and the second part 6b. That is, in the space for unit cell the branch 5b of the counter electrode 5 and the second part 6b of the pixel electrode 6 are alternatively separated by same distance and parallel to the data bus line 3. Between the gate bus line 1 and the data bus line 3 and between the counter electrode 5 and the pixel electrode 6 are interposed a gate insulating layer (not shown). Wherein AP in FIG. 1 designates aperture region of unit pixel.
The problem of the IPS-LCD will be described with reference to FIG. 2 showing a sectional view along IIxe2x80x94IIxe2x80x2 of FIG. 1. The numeral 7 indicates a liquid crystal molecule. When a signal is applied to the branch 5b of the counter electrode 5 and the second part 6b of the pixel electrode 6, there is generated a potential therebetween and thus the liquid crystal molecules are operated. Since the branch 5b of the counter electrode 5 and the second part 6b of the pixel electrode 6 have a given width, there is no electric field thereon. Accordingly, even if the signal is applied, is caused a disclination, the liquid crystal molecules positioned over the branch 5b and the second part 6b being not operated (A solid line represents an equi-potential in FIG. 2). Conventionally, the branch 5b of the counter electrode and the second part 6b of the pixel electrode are made of opaque metal in order to block a light of the area in which the liquid crystal molecules are not operated.
Therefore, the aperture ratio is reduced by the area of the branch 5b and the second part 6b. In detail, the IPS-LCD has an aperture ratio of 40% or less which is lower than that of 50 to 60% in the TN-LCD. The reduction of aperture ration results in the reduction of the transmittance and thus degradation of the brightness of the LCD.
Accordingly, an aim of a present invention is to provide a LCD having a counter electrode and a pixel electrode capable of minimizing an area in which liquid crystal molecules do not operate.
Another aim of the present invention is to provide a LCD having an improved aperture ratio, a transmittance and brightness.
In order to accomplish the aims of the present invention, in the LCD having a gate bus line disposed in a first direction on a substrate, a data bus line disposed in a second direction on the substrate and defining an unit cell space together with the gate bus lines, a counter electrode comprises a first part formed in the unit cell space, made of transparent material, disposed in the second direction and having a sectional view of a substantial triangle shape. Also, a pixel electrode comprises a second part formed in the unit cell space, made of transparent material, disposed in the second direction and having a sectional view of a substantial triangle shape. There is generated an electric filed parallel to the first direction by the first part and the second part. Here, the sectional view of the first part and the second part is a perfect triangle shape or a trapezoid shape. In case of the trapezoid shape, among four sides of the trapezoid shape, the side opposite to the substrate has a width of about 0.01 to about 2 xcexcm. The first part and the second part are made of ITO. The counter electrode further comprises a wiring part arranged in the first direction spaced from the gate bus line. The wiring part and the first part are electrically connected. The pixel electrode further comprises a third part overlapped with a channel layer formed on the gate bus line and a fourth part for connecting the second part to the third part. Here, the wiring part, the third part and the fourth part are made of opaque metal.